Polytetrafluoroethylene fabrics are fabrics woven from strands of polytetrafluoroethylene. Polytetrafluoroethylene is commonly known as Teflon and is a registered trademark of E.I. DuPont Company.
Polytetrafluoroethylene fabrics are available in many varieties from a variety of distributors. Typical of the polytetrafluoroethylene fabrics is a fabric sold by Stern and Stern Textiles, Incorporated, New York, N.Y., called T41-30. It is a lenoweave cloth with 45.times.21 ends/inch and has a thickness of 0.010 inch. It has a weight of 4.35 ounces per square yard.
Polytetrafluoroethylene fabrics are used for a variety of purposes including supports for fluoropolymer ion exchange active films. Such films are commonly used as ion exchange membranes in electrolytic cells.
The prior art has attempted to attach polytetrafluoroethylene fabrics to ion exchange membrane films using heat treatment and extraction procedures rather than stabilizing the cloth itself (see U.S. Pat. No. 4,272,560).
Other known relevant art is known to include: U.S. Pat. Nos. 3,770,567; 3,925,135; 4,272,560; 4,324,606; 4,399,183; 4,341,605; and 4,437,951.
It would be highly desirable to be able to size polytetrafluoroethylene fabrics. The present invention provides such a method.
Ion exchange active fluoropolymer films have been widely used in industry, particularly as ion exchange membranes in chlor-alkali cells. Such membranes are made from fluorinated polymers having ion exchange active groups attached to pendant groups from the polymeric backbone.
Such polymers are usually thermoplastic and may be fabricated into films or sheets while in their molten form using mechanical extrusion equipment.
Forming membrane structures and support structures into multiple layers is the subject of several patents and applications including U.S. Pat. Nos. 3,925,135; 3,909,378; 3,770,567; and 4,341,605. However, these methods use complicated procedures and equipment including such things as vacuum manifolds, rolls and release media.
Burrell states the theory of Bagley [J. Paint Tech., Volume 41, page 495 (1969)] predicts a non-crystalline polymer will dissolve in a solvent of similar solubility parameter without chemical similarity, association, or any intermolecular force. However, he fails to mention anything about the solubility of polymers demonstrating crystallinity.
Currently, it is difficult to attach polytetrafluoroethylene fabrics to ion exchange active membrane films. In fact, as currently practiced, the fabric is only embedded into the membrane film and not attached. Internal voids are left within the threads and at the intersections of the weave.
It would be highly desirable to have a supported ion exchange membrane film supported by a polytetrafluoroethylene fabric where the fabric is more intimately attached and a more integral part of the structure. Such an article is the subject of the present invention.